The present invention generally relates to improvements in combustors and more particularly to an improved fuel/oxidizer mixing and combusting apparatus that is readily integrated into a compact, lightweight, high-performance lift thrust producing and energy conversion devices.
During the development of the Boeing Joint Strike Fighter (JSF) Short Take-Off Vertical Landing (STOVL) aircraft propulsion system, we found it desirable to incorporate a means for providing auxiliary thrust capability to augment the core engine lift thrust. We evaluated numerous propulsion options that were based on conventional combustor technology, but drawbacks associated with each of these options precluded their employment in the STOVL aircraft propulsion system.
These drawbacks were primarily related to the overall length of the combustor, rendering the incorporation of various known propulsion options into the STOVL aircraft propulsion system unpractical due to concerns for weight and packaging. In this regard, it is relatively common for combustors without high total pressure loss instream flameholders to be designed with a length-to-diameter (L/D) ratio of 5 or more, wherein the length of the combustor is defined as being the distance between the combustor dump plane and the nozzle throat. Reductions in the L/D ratio of suitable known combustors was not possible, as a shortening of the combustor""s length would not provide sufficient time for the fuel and air (oxidizer) to mix and combust prior to their discharge through the nozzle.
In one preferred form, the present invention provides a fuel/oxidizer mixing and combusting apparatus having a combustor and a swirl generator. The swirl generator includes an inlet housing, a swirl vane pack, a centerbody assembly and a plurality of fuel injectors. The inlet housing is coupled to the combustor inlet and defines a hollow interior volume that intersects the combustor inlet at a dump step. An oxidizer flow having a velocity that is substantially defined by an axial velocity component is conducted through the hollow interior volume. The swirl vane pack is disposed within the hollow interior volume and includes a plurality of vanes that cooperate to change the velocity of the oxidizer flow so that it includes a substantial tangential velocity component. The centerbody assembly is disposed in the hollow interior volume and coupled to the swirl vane pack such that it extends rearwardly from the swirl vane pack. The fuel injectors are coupled to at least one of inlet housing, the swirl vane pack and the centerbody and dispense fuel therefrom. The swirl generator converts the oxidizer flow received therein into a swirling, three-dimensional flowfield, a first portion of which flows over the dump step to form an outer recirculation zone and a second portion of the flowfield forms a central recirculation zone that is anchored by an aft end of the centerbody assembly. A first portion of the fuel mixes with the first portion of the flowfield to fuel the outer recirculation zone and a second portion of the fuel mixes with the second portion of the flowfield to fuel the central recirculation zone.
In another preferred form, the present invention provides an apparatus comprising a combustor and a swirl generator, the swirl generator is coupled to the inlet of the combustor and is operable for converting an oxidizer flow with a velocity that is substantially completely defined by an axial velocity component into a three-dimensional flowfield that includes a substantial tangential velocity component. The swirl generator includes a flow defining means and a fueling means. The flow defining means is operable for controlling both a toroidal outer recirculation zone and a central recirculation zone that is disposed inwardly of the outer recirculation zone in the combustor. The fueling means is operable for fueling the outer and central recirculation zones. Heat and combustion by-products produced during combustion are carried upstream by the outer and central recirculation zones where the heat and combustion by-products are employed to continuously ignite a combustible fuel/oxidizer mixture in a shear layer adjacent each of the outer and central recirculation zones.
The present invention overcomes the aforementioned drawbacks by providing a fuel/oxidizer mixing and combusting apparatus that permits extremely rapid fuel atomization, vaporization and mixing with a combustion efficiency that is ranges from about 90% to about 99%. Consequently, we were able to reduce the length of the combustor to attain L/D ratios substantially less than that which was attained by the known combustors.
In yet another preferred form, the present invention provides an apparatus for providing propulsive power having an inlet structure, a swirl generator and a combustor. The inlet structure is configured to conduct an oxidizer flow therethrough and includes a plurality of flow guiding vanes that cooperate to affect the oxidizer flow such that it is substantially uniform and axial. The swirl generator is coupled to an aft end of the inlet structure and includes a flow affecting means and a fueling means. The flow affecting means includes a plurality of vanes, a dump step and a centerbody with an aft end that terminates rearwardly of a root of the vanes. The flow affecting means is operable for converting the axialsymmetric oxidizer flow into a three dimensional flowfield that includes a substantial tangential velocity component. The flow affecting means is also operable for forming and controlling both a toroidal outer recirculation zone, which is anchored by the dump step, and a central recirculation zone, which is disposed inwardly of the outer recirculation zone and anchored by the aft end of the centerbody. The fueling means is operable for fueling the outer and central recirculation zones and a core flow. The combustor coupled to an aft end of the swirl generator and includes a nozzle. Heat and combustion by-products produced during combustion are carried upstream by the outer and central recirculation zones where they are employed to continuously ignite a combustible fuel/oxidizer mixture in a shear layer adjacent each of the outer and central recirculation zones. Combustion by-products from the core flow are expelled through the nozzle to produce thrust.
The present invention overcomes the aforementioned drawbacks by providing an apparatus for providing propulsive power that utilizes swirl combustion in a manner that significantly reduces the overall weight and size of the apparatus relative to other propulsion devices that employ conventional combustor technology. The apparatus of the present invention is compatible with the throttle range of a conventional gas turbine engine, provides smooth combustion with no instabilities with minimum total pressure losses, enables significant reductions in the L/D ratio of the combustor relative to the known combustors and is readily packaged into various applications. Other benefits over the known art include simplicity, reliability, wide flammability limits and high combustion efficiency and high thrust performance. Furthermore, the apparatus of the present invention provides substantial flexibility to retune existing combustor designs to meet specific combustor requirements.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.